1. Field of the Invention
The present invention relates to a thermal transfer type printer, particularly, relates to a driving system of a thermal transfer type printer, in which, the motion of a thermal printing head to and from the printing paper, the feeding of the printing paper, and the feeding of the ink ribbon are driven by a common motor.
2. Description of the Prior Art
Japanese Patent Application JP-A-7-76150 discloses such a driving system of a thermal transfer type printer in the prior art. FIG. 10 is a side view of the driving system of the thermal transfer type printer of the prior art disclosed in it, showing the initial state (a) and the printing state (b).
Reference numerals 101 denotes a motor gear connected to a motor (not shown), and the reference numeral 102 denotes a transmission gear group. The transmission gear group 102 includes an intermittent gear 102a engaging with the motor gear 101, a swing-down gear 102b, a swing-up gear 102c, a bracket 102d rotatable around the rotation axis of the intermittent gear 102a, on which the three gears 102a, 102b, and 102c are mounted, and a spring (not shown) disposed between the swing-down gear 102b and the bracket so as to form a clutch which transmits torque only when the torque exceeds a predetermined value. They are so arranged that the transmitting gear group as a whole swings around the axis, due to the action and reaction of this spring, according to the rotation of the intermittent gear 102a.
Reference numeral 103 denotes a cam gear. The cam gear 103 includes grooves 103a, 103b, which are formed on the peripheral by cutting off the teeth, and a cam groove 103c formed on the side face. The cam gear 103 can engage with the swing-down gear 102b and the swing-up gear 102c. However, the cam gear 103 can cut off the transmission of torque, when the swing-down gear 102b falls into the groove 103b and the swing-up gear 102c falls into the groove 103b.
Reference numeral 104 denotes a head arm, which can pivot around an arm axis 104b. One end of the head arm 104 contacts with a cam shaft 104a, and the other end of the head arm 104 contacts with a thermal printer head 106 through a spring (not shown). A head fixing member 105, on which the thermal printer head 106 is fixed, is free-rotatably disposed on the arm axis 104b. A plurality of heating elements arranged in the main scanning direction are disposed on the thermal printer head 106. The swing-up gear 102c can be connected through a connecting gear 107 to a gear 108, which is connected with a platen roller gear 109. The platen roller gear 109 is fixed to the axis of the platen.
The platen roller gear 109 of the platen roller 110 is connected with a clutch gear 113 of an ink ribbon winding up reel 126 through connecting gears 111, 112. The ink ribbon 123 is supplied from an ink ribbon supplying reel 125 and is wound up by the ribbon winding up reel 126 after passing through a path between the thermal printing head 106 and the platen roller 110.
Web paper 122 is supplied from a rolled web 118, which is a paper wound around a web reel 124. A winding-back gear 120 is disposed co-axially with the cam gear 103 so that they can rotate separately. However, the winding-back gear 120 can engage with the cam gear 103, when the swing-up gear 102c falls into the groove 103b. Namely, the rolled web 118 can be driven to rotate by the core gear 119, when it engages with the cam gear 103 through the winding-back gear 120.
The function of the thermal transfer type printer of this prior art is explained below.
When the motor gear 101 rotates in the normal direction (clockwise in the figure) starting from the state shown in FIG. 10(a), the transmission gears 102 rotate as a whole in the reverse direction (counter clockwise) so that the cam gear 103 engages with the swing-down gear 102b. Now, the bracket 102d of the transmission gears cannot rotate counter clockwise. And the swing-down gear 102b begins to rotate clockwise, resisting a resilient force of a spring (not shown).
The cam gear 103 rotates counter clockwise, due to the engagement with the swing-down gear 102b. Then the cam shaft 104a of the head arm 104 moves along the cam groove 103c from an inner position to an outer position in the side face of the cam gear 103. According to this movement of the head arm 104, the thermal printing head 106 approaches towards the platen roller 110, pivoting around the arm axis 104b.
The thermal printing head 106 contacts with the platen roller 110, then a spring (not shown) disposed between the head arm 104 and the head fixing member 105 presses the thermal printing head 106. The cam gear 103 rotates until the swing-down gear 102b falls into the groove 103a.
When the swing-down gear 102b falls into the groove 103a, the rotation of the cam gear 103 stops. In this state, the swing-up gear 102c is engaging with the gear 107. In this state, so-called "head down state", the power is transmitted through the gear 107, gear 108, platen gear 109 so as to drive the platen roller 110 to rotate counter clockwise.
At this state, the web 122 and the ink ribbon 123 between the platen roller 110 and the thermal printing head are fed and the web paper is printed by heating the thermal printing head. In this process, the clutch gear 113, engaging with the platen gear 109 through the gear 111 and 112, rotates to drive the ink ribbon winding up reel 126 through a sliding clutch. Accordingly, the ink ribbon is wound up around the ink ribbon winding up reel 126 under a predetermined tension.
When the printing finishes, the motor (not shown) rotates in the reverse direction so as to rotate the motor gear 101 counter clockwise. Then the transmission gear group 102 as a whole rotates clockwise, so that the swing-up gear 102c separates from the gear 107 and engages with the cam gear 103. According to the further rotation of the motor, the cam gear 103 rotates clockwise so that the head arm 104 moves to the inner position and the thermal printing head 106 separates from the platen roller 110.
The cam gear 103 stops, when the swing-up gear 102c falls into the groove 103a of the cam gear 103. In this moment, the swing-up gear 102c engages with the winding-back gear 120 so that the core gear 119 engaging with the winding-back gear 120 rotates. The printed web 122 is wound back according to the rotation of the rolled web 118, which is fixed to the core gear 119. As a result, the states of the web and the printer come back to the initial state. In case of color printing, these processes are repeated for each color.
Such a thermal printer of the prior art has drawbacks that the thermal printing head 106 separates from the platen roller 110, when the web is wound back. Namely the web 123 is in free state, when it is wound back. As a result, a slip between the thermal printing head 106 and the web 122 occurs for every winding back of the web, which causes a shift of the register in the color printing.
Moreover, the feeding of web is carried out only by the platen roller 110 in the printing procedure, thus, the holding force of the web is small. As a result, a subtle slip between the web 122 and the platen roller 110 occurs during the printing procedure, namely, the feeding amount of the web cannot be exactly controlled.
Further, the thermal printer in the prior art is applicable only to web type paper, and sheet type paper can not be used.